Mortise locks are well known devices used to latch swinging doors in a closed position. A typical mortise lock includes a lock body in which the moving components of the lock are disposed and a strike plate. The lock body is typically installed in a mortise (or pocket) that has been cut in the material of a door. The strike plate is typically installed on the doorframe in a position appropriate for it to interact with the lock body. The strike plate includes one or more openings for receiving one or more latches or deadbolts from the lock body. These latches and deadbolts serve various purposes but generally are intended to latch or lock the door in a closed position.
Mortise locks usually include a latch for securing a door in a closed position. The latch has an extended position in which the latch protrudes from the lock body and into an opening of the strike plate. The latch can be moved into a retracted position by turning the door handle which permits the door to be opened. In many locks, the latch is biased by a spring into the extended position.
Mortise locks also often include a deadbolt to secure the closed and latched door against attempts to force the door open. Typically, a deadbolt is extended and retracted by the rotational movement of a lock cylinder in the lock body. When the lock cylinder is rotated, the deadbolt moves between a retracted position in which the deadbolt is within the lock body, and an extended position in which the deadbolt protrudes from the lock body and into an opening of the strike plate. Because the deadbolt is typically constructed using strong, durable materials, it provides better resistance to attempts to open the door by force than a typical door latch.
The need to secure a door against forcible attempts to open it takes on enhanced importance in some applications. For example, in detention-type applications, in which possibly violent and/or dangerous persons must be detained behind a swinging door, the strength of a deadbolt to resist force becomes paramount. Other applications include residential doors in high-crime areas, designated “safe rooms” in schools, houses, or other buildings, and various applications related to military, law enforcement, and correctional facilities.
Standards organizations—such as ASTM International—have developed test methods and standards for classifying the strength of bolt designs. (Throughout this application, the term “bolt” is used to refer generically to both deadbolts and latches). These include standards for detention and correctional facilities. For example, STM Standard F1577 relates to standard test methods for detention locks for swinging doors. Among these standard tests is an impact test designed to evaluate the capability of a detention lock to resist repeated impact forces.
The need for high-strength bolt assemblies has been typically addressed by using higher strength materials for the deadbolt, latch, and/or other impact bearing components. Other approaches use larger sized components, such as a larger deadbolt or latch, to increase the strength of the lock. These approaches have been generally unsuccessful. It has become apparent that the overall size of a door lock intended to be handled by humans imparts a practical limit on how strong a conventional deadbolt or latch can be. There is a limit on the size that a deadbolt or latch can be for use in such a door, such that even use of the strongest material is not sufficient to withstand impacts that may be applied to the door. These traditional approaches to higher strength locks are not known to conform to known standards for detention and correctional facilities.
Accordingly, there is a need in the art for a lock design with improved resistance to forceful impacts. What is needed is a lock design that conforms to known standards for high-strength deadbolt assemblies. What is further needed is for such a design to be usable with typical mortise lock arrangements for swinging doors. What is further needed is for such a design to be simple and inexpensive to manufacture and install.